Improvement in Bond Strength of Steel Bar in Geopolymer Concrete by Adding Graphene Nanoplatelets

The bond strength of steel reinforcement bars in concrete is of prime importance for the strength and serviceability of reinforced concrete structures. The composition of concrete directly affects the bond strength of steel bars in concrete. Research is ongoing to improve the bond properties of concrete with the addition of nanoparticles. In this paper, the effect of adding graphene nanoplatelets (GNP) to geopolymer concrete on the bond strength of steel bars in geopolymer concrete was investigated and compared with the bond strength of steel bars in ordinary portland cement (OPC) concrete. Slag and fly ash were used as aluminosilicate precursors, and ambient curing conditions were adopted for preparing geopolymer concrete. Specimens were cast with geopolymer concrete without and with GNP and OPC concrete without and with GNP. Steel bars of four different diameters (10, 12, 16, and 20 mm) were used for preparing the specimens. The quantity of GNP added in the concrete was 0.5% by weight of aluminosilicate materials in geopolymer concrete and 0.5% by weight of cement in OPC concrete. The addition of GNP to geopolymer concrete enhanced the bond strength by 13%-19% for the steel bars of diameters 10-20 mm. The bond strengths of steel bars in geopolymer concrete were found to be lower than the bond strength of steel bars in OPC concrete. Furthermore, the bond strengths were calculated using equations available in the design codes and available research studies on geopolymer and OPC concrete and compared with the experimental bond strengths.